1. Field of the Invention
The present invention relates to a technique for manufacturing a semiconductor device, and more particularly to a technique for exposure.
2. Description of the Background Art
Semiconductor devices are continuously becoming miniaturized, and the numerical aperture (NA) of exposure apparatuses is being increased for further miniaturization.
However, as NA is getting higher, the angle of incidence on a target of exposure, e.g., a photoresist increases, which causes the effects of polarization which have been neglected to become evident. This causes degradation in imaging characteristics in the photoresist. Such circumstances are introduced in “Challenges in high NA, polarization, and photoresists” by Bruce W. Smith, et al., SPIE 2002, 4691-2, pp. 11-24. The following documents are related to the present invention: “Polarizing & Retardation Films” retrieved on May 15, 2003 from the Nitto Denko homepage <URL:http://www.nitto.co.jp/product/industry/electronics/output/lcds/polar/index.html>; Japanese Patent Application Laid-Open No. 5-226225 (1993); and Japanese Patent Application Laid-Open No. 2001-185476.
Optical systems of usual exposure apparatuses have not been able to control polarization of diffracted light generated through a mask pattern, so that polarized light incident on a photoresist includes p-polarized light and s-polarized light in an even ratio. With an increase in NA of exposure apparatuses, the angle of incidence on a target of exposure, i.e., a photoresist increases as described above, causing the ratio of p-polarized light and s-polarized light incident on the photoresist to vary. Further, since the contrast of an optical image differs between p-polarized light and s-polarized light, the contrast of an optical image generated by composition of p-polarized light and s-polarized light is degraded. Then, improvement in the degree of resolution cannot be expected even where NA is increased.